Compared with a first generation of semiconductors with silicon (Si) as a typical example and a second generation of semiconductors with gallium arsenide (GaAs) as a typical example, silicon carbide material, as a typical one of a third generation of semiconductors, has a larger band gap and a higher critical breakdown electric field strength, and is thus suitable to produce high-voltage large-power semiconductor devices. As a research focus in international power electronic device and new material fields, silicon carbide has been drawing high attention in academic field, and has entered commercial stage under promotion of Cree, Rohm, Infineon and other companies.
As to a power device with a high performance and a high reliability, it should have a high enough voltage resistance ability to bear connection and disconnection of a main circuit at a high voltage. Meanwhile, the power device should have an on-resistance as low as possible so as to reduce working loss thereof and meet requirements of high efficiency, environmental friendly, and energy conservation. Compared with a silicon-based MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) with a same power level, a silicon carbide MOSFET has a much lower on-resistance and switching loss, and is more suitable to work at a higher frequency. Moreover, by virtue of its capability of withstanding high temperature, stability of a silicon carbide MOSFET at high temperature has been greatly improved.
However, it should be noted that, a critical breakdown electric field strength of the silicon carbide MOSFET device can reach 2 MV/cm to 3 MV/cm, which is different from the silicon-based MOSFET device. According to the principle of continuity of electric flux at oxide interface, when the device works at a high voltage, an electric field strength of a gate oxide layer above a JFET (Junction Field Effect Transistor) region may easily exceed 4 MV/cm, which seriously affects reliability of the gate oxide layer. With respect to a silicon carbide MOSFET power device, if a width of the JFET region is too small, an on-resistance thereof will become over large; while if the width thereof is too large, a concentrated effect of an electric field curvature will become significant, and a breakdown voltage of the device will drop. Therefore, during design of the silicon carbide MOSFET device, in order to inhibit electric field concentration in the gate oxide layer and ensure reliability thereof, the on-resistance property of the device is usually sacrificed. That is, during design of the silicon carbide MOSFET device, a small JFET region width, a high P well doping concentration, and a large P well junction depth are adopted. However, according to the improvement methods in the prior art, on the one hand, the on-resistance of the device would be increased; and on the other hand, high-dose of Al ions need to be injected therein using high energy, which increase manufacturing difficulty thereof, and is not conducive to reduction of the working loss.